Preparation of benzene derivatives



Patented Jan.

PATENT OFFICE PREPARATION or- BENZENE DERIVATIVES Courtney Conover and Arthur E. Huff, St. Louis;

Mo., assignors to. Monsanto Chemical Company, St. Louis, Mo., a corporation or Delaware No Drawing. Application July 19, 1 935,

Serial No, 32,236

9 Claims.

The present invention relates to the dehydrogenation of aromatic compounds to form polya'ryls therefrom, and it has particular relation to vapor phase pyrogenetic processes therefor.

The main objects of the invention are to pro-- vide l v A process .of'dehydrogenatlng aromatic coma pounds to form poly-aryls in which. exceptionally high conversion per cycle of contact. with the heat transfer body is obtained. w i

A process of the above designated character which is simple, ,eiiicient of operation and which can be conducted at.butslightexpense with apparatus' heretofore employedin conducting reactions of this character. l ,Theseand other objects willbe apparent from perusal of the appended specification and claims.

It has heretofore been proposed to form diand'higher pol-y-aryls such as diphenyl and triphenyl and t he like, such as meta diphenyl phena ylene, by passing vapors of benzene, or alkylated benzene and other simplehydrocarbon derivatives of benzene at high velocity through a cracking tube or directly through a heat transfer medium comprising a suitable relatively inert, rela- Aftereach contact with theheat transfer medium.

the reaction mixture consisting of unreacted aromatic compounds and the products resulting from the reaction, such as diphenyl and diphenyl phenylene, etc., was condensed and then distilled to separate the components of .the mixture. The unreacted material was then subjected to recycling for purposes of converting itinto more of the benzene derivatives.

The present invention is based on the discovery that certain partially oxidized or reacted aromatic or aliphatic hydrocarbonsand particularly those containing one or more oxygen atoms exert a favorable influence when introduced into benzene or alkylated benzene prior to the pyrolysis, by reason of a remarkable increase in poly-aryl formation per cycle.

Among the classes of oxy-aliphatic compounds which may be employed with vapors of benzene and derivatives of benzenes to promote the con version thereof are included the following:

(A) Alcohols of the type expressed by the forcompounds selected from different classes from i (A) to (F) or of two or more members of the mula ROH whereR is analiphatic or-aromatic group. This group of compounds includes: methyl alcohol, ethyl alcohol, isopropyl alcohol and the isomers thereof. Secondary, 'butyl alcohol and its isomers, amyl alcohols, phenol cyclohexanol, glycol, etc. i r

(B) Aldehydes of thetype RCHO where R is hydrogen or an aliphatic hydrocarbon group. This class includes: formaldehyde, acetaldehyde, propyl aldehydabutyi aldehyde andfurfural. 10

(C), Keto'nes of the type RCOR', where R and R are ,like or unlike aliphatic hydrocarbon groups. This class includes acetone and ethyl methyl, ketone.

. (n) Aliphatic acids of thetype Rcoon where 15 R is hydrogen or an aliphatic hydrocarbon group. This class includes: formic acid, acetic acid, propionic acid and butyric, acid.

(E) Acid esters of the type RCOOR' where R and R are like or unlike, aliphatic hydrocarbon groups or R is hydrogen and R) is an aliphatic hydrocarbon radical. This class includes: methyl acetate, ethyl acetate, propyl, acetate and. ethyl formate. l j

(F) Ethers of the formula ROR', where R and 25 R are like or unlike aliphatic hydrocarbon groups. This class incudes: methyl ether, ethyl ether and ethyl methyl ether. i

Mixtures of any two or more of the above same class are also included within the scope of the invention.

. Incontrastto the foregoing activators which in each case may be considered partially oxidized r,

hydrocarbons, the addition of hydrocarbons themselves, notably aliphatic and heterocyclic diphenyl or homologue of diphenyl per pass, through the molten bath.

These conditions are well understood in the art and it is not believed to be necessary to refer to them in great detail. For example,a temperature of thebath within the range of 700-850 C. is satisfactory. Even these values do not constitute the extreme range because higher temperatures, so long as they do not cause excessive cracking and nuclear decomposition of the products, may also be employed withinthe purview of the invention. Lower temperatures are likewise contemplated, although, of course, the yield obtained per pass through the molten bath under such conditions is lowered.

The amount of the promoter employed in conducting the reaction may vary over a relatively wide range. As much as 2% by weight or more may be employed; however, excellent results are ialso obtained and with greater economy with amounts of only 0.1 of 1%. Probably with such compounds as isopropyl alcohol, ethyl alcohol, acetone and diethyl ether, best results are obtained where one to two tenths of a per cent are used.

The conversion per pass may be increased to a limited extent by subjecting the reaction bath to moderately vigorous agitation. However, agitation is by no means an essential feature of the invention.

The ratio of diphenyl and higher boiling homologues thereof, such-as diphenyl phenylene or isomers of diphenyl phenlyene, is controllable to some extent by varying the percentage of conversion of benzene per'pass through the molten bath. It is found that the higher the conversion the higher the percentage of diphenyl homologues obtained.

The process as thus disclosed is applicable to the higher homologues of benzene, including toluene and xylene; naphthalene is likewise included. Also the simpler nuclear substituted derivatives of benzene, toluene, xylene and naph thalene, such as mono and di-chloro and bromo substituted compounds may be employed in conducting the reaction.

In conducting a series of typical runs in accordance with the provisions of the present invention, a temperature of about '750-800 C. in the bath was employed.

' To illustrate the advantages of our typical invention, the following results are given of experiments which were made under identical conditions,"each difiering'from the other only in that the benzene which was recycled-contained different catalysts or promoters.

Re-run benzene was employed, the rate of feed was 22 to 28.3 pounds of benzol per hour. In each case approximately two per cent by weight of promoter was employed.

In contrast with the foregoing, dicyclopentadiene impeded or inhibited diphenyl formation; the amount formed under comparable con ditions being 8.6%.

From the foregoing examples it will be apparent that by employing promoters of the reaction of the type herein described, increases inthe percentage of conversion per pass of benzene in the molten bath, amounting to in some cases as much as 100 or 200% or more, are obtained. This, of course, means that the number of passes required completely to convert benzene into diphenyl or diphenyl homologues is greatly reduced and that the attendant expense involved in repeatedly heating the benzene to vaporize it and subsequently condensing the reaction product to admit of recovery of the homologues is proportionately reduced. There is also a corresponding reduction in the amount of space and apparatus required, and of the labor required to attend such apparatus.

Use of the promoters is not confined to use of molten baths as heat transfer media but is also applicable to processes in which the benzene is simply passed through heated tubes of metal or refractory material.

It is to be specifically understood that the present invention is not limited to any specific mode of pyrolysis and that while the results obtained with lead cracking have been given for the purpose of illustrating the advantages to be gained, the invention is not so limited, but contemplates also vapor phase tube cracking wherein turbulent flow conditions obtain.

Although we have shown. and described only the preferred embodiments of the invention, it will be apparent to those skilled in the art that numerous modifications may be made therein without departure rrom the spirit of the invention or from the scope of the appended claims.

The expression pyrolysis" is used herein to designate high temperature reactions wherein promoters activate or accelerate the process, and not in the more restricted sense of the term, sometimes used in texts, which excludes the presence of catalytic bodies.

What we claim is:

1. A method of treating aromatic hydrocarbons containing single benzene nuclei which oiomprises passing vapors thereof at the temperature of dehydrogenation through a molten bath of non-reactive, non-volatile material in the presence of catalytic quantities of a reaction promoter comprising a volatile aliphatic compound containing at least one oxygen atom.

2. A method as defined in claim 1, in which the molten bath comprises lead.

3. A method of forming diphenyl and homologues of diphenyl which comprises subjecting benzene to contact with a bath of non-reactive, non-volatile material, at a temperature sufficient to efiect dehydrogenation of the benzene and in the presence of an organic oxidation derivative of an aliphatic hydrocarbon.

4. A method of preparing diphenyl and homologues of diphenyl which comprises bubbling benzene vapors through a molten bath of refractory, non-volatile material at the temperature of dehydrogenation of the benzene and in the presence of a partially oxidized aliphatic hydrocarbon which still contains combined hydrogen,

5. A process as defined in claim 4, in which the oxidized hydrocarbon is an alcohol.

6. A process as defined in claim 4 in which the oxidized hydrocarbon is a ketone.

' 7. A process as defined in claim 4 in which the oxidized hydrocarbon is an ether.

8. A process of forming diphenyl and homologues of diphenyl which comprises heating a materialfrom a class consisting of benzene and alkylated benzene in vapor phase to the temperature of dehydrogenation in the presence of a partially oxidized aliphatic hydrocarbon which still contains combined hydrogen.

9. A process of preparing diaryl compounds containing two aryl nuclei directly joined which comprises heating vapors of an aryl compound to the temperature of dehydrogenation in the presence of a. volatile organic compound containing a carbonyl group and. combined hydrogen. 

